1. Field of the Invention
The invention relates to aluminum based, silicon containing, alloys having strength, ductility and toughness at ambient and elevated temperatures and relates to powder products produced from such alloys. More particularly, the invention relates to Al-Fe-Si alloys that have been rapidly solidified from the melt and thermomechanically processed into structural components having a combination of high strength, ductility and fracture toughness.
2. Brief Description of the Prior Art
Methods for obtaining improved tensile strength at 350.degree. C. in aluminum based alloys have been described in U.S. Pat. Nos. 2,963,780 to Lyle, et al.; U.S. Pat. No. 2,967,351 to Roberts, et al.; and U.S. Pat. No. 3,462,248 to Roberts, et al. The alloys taught by Lyle, et al. and by Roberts, et al. were produced by atomizing liquid metals into finely divided droplets by high velocity gas streams. The droplets were cooled by convective cooling at a rate of approximately 10.sup.4 .degree. C./sec. As a result of this rapid cooling, Lyle, et al. and Roberts, et al. were able to produce alloys containing substantially higher quantities of transition elements than has hither to been possible.
Higher cooling rates using conductive cooling, such as splat quenching and melt spinning, have been employed to produce cooling rates of about 10.sup.5 .degree. to 10.sup.6 .degree. C./sec. Such cooling rates minimize the formation of intermetallic precipitates during the solidification of the molten aluminum alloy. Such intermetallic precipitates are responsible for premature tensile instability. U.S. Pat. No. 4,379,719 to Hildeman, et al. discusses rapidly quenched aluminum alloy powder containing 4 to 12 wt % iron and 1 to 7 wt % cerium or other rare earth metal from the lanthanum series.
U.S. Pat. No. 4,347,076 to Ray, et al. discusses high strength aluminum alloys for use at temperatures of about 350.degree. C. that have been produced by rapid solidification techniques. These alloys, however, have low engineering ductility and fracture toughness at room temperature which precludes their employment in structural applications where a minimum tensile elongation of about 3% is required. An example of such an application would be in small gas turbine engines discussed by P. T. Millan, Jr.; Journal of Metals, Volume 35(3), page 76, 1983.
Ray, et al. discusses aluminum alloys composed of a metastable, face-centered cubic, solid solution of transition metal elements with aluminum. The as cast ribbons were brittle on bending and were easily comminuted into powder. The powder was compacted into consolidated articles having tensile strengths of up to 76 ksi at room temperature. The tensile ductility or fracture toughness of these alloys was not discussed in detail in Ray, et al. However, it is known (NASA REPORT NASI-17578 May 1984) that many of the alloys taught by Ray, et al., when fabricated into engineering test bars do not posses sufficient room temperature ductility or fracture toughness for use in structural components.
Thus, conventional aluminum alloys, such as those taught by Ray, et al. have lacked sufficient engineering toughness. As a result, these conventional alloys have not been suitable for use in structural components.